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Function assignment of external terminal and control
4.15.5 Magnetic flux decay output shutoff signal (X74 signal)
Performing frequent start/stop (inching operation) during Real sensorless vector control may cause an inverter
fault (electronic thermal relay function fault: E.THT, etc) due to residual magnetic flux and an error in monitor
output (running speed, motor torque, load meter, torque command, torque current command, motor output).
In such a case, use magnetic flux decay output shutoff signal (X74) as output shutoff signal.
Turning X74 signal ON shuts off output after decaying motor residual magnetic flux.
.............. Specifications differ according to the date assembled. Refer to page 491 to check the SERIAL number.
For the X74 signal, set "74" in any of Pr. 178 to Pr. 189 (input terminal function selection) to assign the function.
Operate a mechanical brake after turning X74 signal ON.
When the MC is provided on the inverter output side, turn X74 signal ON and open the MC after magnetic flux decay
operation time (refer to below) has elapsed.
Inverter output voltage shutoff timing
X74 signal
X74
Output voltage
RUN
Mechanical brake
MC on the output side
* Maximum time of magnetic flux decay operation
Motor Capacity
(Pr. 80 setting)
Magnetic flux decay
processing time
REMARKS
When performing operation other than Real sensorless vector control, turning X74 signal ON immediately shuts off inverter
output.
During an automatic restart after instantaneous power failure or start-time online auto tuning under Real sensorless vector
control, turning X74 signal ON immediately shuts off inverter output.
When some other factor affecting output shutoff (inverter alarm, MRS signal ON, etc.) occurs during magnetic flux decay
operation, magnetic flux decay operation is stopped to immediately shut off output.
Pr.850 Brake operation selection is also available to enable the magnetic flux decay output shutoff.
CAUTION
Changing the terminal assignment using Pr. 178 to Pr. 189 (input terminal function selection) may affect the other functions. Set
parameters after confirming the function of each terminal.
Different from MRS signal, voltage is output during magnetic flux decay processing even if X74 signal turns ON. Take care not
to have an electrical shock.
If the timing of mechanical brake opening is early, motor shaft may be forced to turn by a gravity drop or external force. If the
timing of mechanical brake opening is late, overcurrent, stall prevention operation or electronic thermal relay function may be
activated. Use output frequency detection signal (FU) or output current detection signal (Y12) to perform the mechanical brake
opening suitable for the machine.
242
ON
Magnetic flux decay
processing time
ON
ON
ON
ON
Do not turn off MC
during this processing time
2.2kW or less
3.7kW to 11kW
250ms
500ms
MRS signal
MRS
*
Output voltage
RUN
Mechanical brake
MC on the output side
15kW to 30kW
37kW to 55kW
800ms
900ms
ON
ON
ON
ON
ON
75kW or more
1100ms
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